The use of brush elements to effect a seal between rotating members dates back to the early part of this century; for example, see U.S. Pat. No. 885,032. Although various methods are available for the production of brushes, two basic methods are now generally employed in the production of brush seals for rotating elements--particularly as such seals are employed in turbo-machinery. The first such method can be described as the "bundle and place" method, and is exemplified by the varying techniques shown in U.S. Pat. Nos. 2,672,640; R.E. 30,206; 4,274,575 and 4,678,113. The differing procedures shown in these patents have two elements in common, they: (i) first form a bundle composed of a multitude of bristles by employing some method of holding the bristles substantially parallel to each other, and thereafter (ii) employ a procedure for placing the bundle onto an annular backing member and joining the bundles to the backing member, to make up the seal. The other well-known method employs a winding machine to rapidly wind the wire onto a mandrel; wherein (i) the mandrel itself may be the backing member which will form the brush seal, i.e., as shown in U.S. Pat. Nos. 4,204,629, 4,642,867 and 4,732,339, or (ii) the wound mandrel is used to hold the multitude of bristles for subsequent placement onto the annular backing ring, as shown in U.S. Pat. No. 4,730,876.
The winding procedures appear to offer significant advantages because of their suitability to rapid production and automation. However, they have proven unsuitable in the production of small diameter brush seals because long lengths of wound bristles are unsuitable to achieving the required bristle inclination relative to the backing member. Thus, the bundle and place method is essentially mandated in the production of small diameter (e.g., 7 to 15 cm) brush seals. Moreover, winding around the backing member dictates that a significant portion of the wrapped wires be scrapped--after cutting. When employed in turbine engines, the strands which form the brush are normally expensive, high temperature, exotic metal alloys or ceramics--such that the scrapped material adds significantly to the cost of production.
U.S. Pat. No. 4,730,876, the disclosure of which is incorporated herein by reference, describes what may be termed a hybrid of the "winding" and "bundle and place" methods. The procedure shown in this patent first winds the wires around a mandrel. After winding, the portion of the wire wrapped around the mandrel is bound together by a flexible clamping member to form a linear array of juxtaposed, parallelly aligned bristles. The resultant, flexible linear array may then be placed on a backing ring (as shown in FIG. 4 of that patent), in an attempt to provide the benefits (e.g. less scrap, small diameter rings) of the "bundle and place" method. The linear array of bristles produced by the method of this '876 patent is composed of two distinct leaves of bristles, which result from winding the bristles over a mandrel and subsequently forcing the leaves together by the flexible clamping member. Inherent in such a clamping procedure is the diminished ability to maintain the requisite bristle packing density and bristle inclination--both of which are critical for brush seals used to effect requisite sealing between the various stages of a turbine engine. If the clamping member is designed to be of a material and structure rigid enough, both to hold the wound bristles in a "tight-packed" arrangement and to maintain the requisite inclination (e.g. about 73.degree. with respect to the mounting member) then the member will inherently be difficult to bend to the desired contour--particularly contours having a small radius of curvature. Conversely, if the member is designed to be comparatively flexible, it will then be difficult to maintain the above-stated objectives of tight-packed bristles, all of which are inclined at the requisite angle.